I was using LiveTrack/Live Event Sharing for a recent 50mi/6hr (with stops) bike ride. The Live Event Sharing notifications were sent to members of my family and myself (phone was with me).
I had my lap distance set to 5mi and was receiving the Event Sharing text as expected every lap with the text notification showing up on the watch face. About 2/3s through the ride, each time I received the Event Sharing lap text, the watch screen would blank out until the text notification timed out or the notification was cleared via an Edge 840. I haven't been able to replicate the issue on much shorter activities.